1. Field of the Invention
The present invention relates to a substrate processing system for performing processing for a substrate.
2. Description of the Related Art
Conventionally, processing for a substrate, for example, a semiconductor wafer or the like often includes a plurality of processes, and the processing is continuously performed using a plurality of processing units. Accordingly, the substrate processing is typically performed in a substrate processing system in which a plurality of processing units are collectively installed.
For example, a substrate processing system for performing the photolithography process includes a loader/unloader section for carrying-in/out the substrate and a processing station for performing the processing for the substrate. At the central portion of the processing station, a central carrier unit is provided around which a plurality of processing unit groups are circularly arranged (Japanese Patent No. 2919925). Each of the processing unit groups is composed of a plurality of different kinds or the same kind of processing units which are multi-tiered. A plurality of substrates sequentially carried-in from the loader/unloader section are sequentially carried to predetermined processing units in the plurality of processing unit groups so that the substrate processing including the plurality of processes is continuously performed. The substrate for which the processing in the plurality of processes has been finished is returned to the loader/unloader section. According to the substrate processing system, the kinds and order of the processing units to which the substrate is carried by the central carrier unit can be changed to flexibly deal with various substrate processing recipes.
According to the above-described substrate processing system, however, the one central carrier unit is used to carry many substrates, and therefore, during carriage of one substrate, the carrier unit cannot carry another substrate in some cases. For this reason, it is difficult to carry out the substrate from the processing unit at an ideal timing at all times, thereby possibly increasing the periods of some substrates staying in the processing units to cause a processing time difference among the substrates. For example, the thermal processing time difference greatly affects the processing result of the substrates and can cause variations in quality of the substrates. Further, if the carriage waiting time of the substrate is increased, the time required for the whole processing of the substrate accordingly increases, and the increase can lead to a reduction in throughput.
Furthermore, a large central carrier unit is located at the center of the processing section, and processing unit groups are arranged around the carrier unit in a manner to keep an operation space for a carrier arm in the conventional substrate processing system. Therefore, a relatively large space is required for the processing station, resulting in a large substrate processing system as a whole.